The present disclosure relates to the subject matter disclosed in international application PCT/EP 98/00641 of Feb. 6, 1998, the entire specification of which is incorporated herein by reference.
The present invention relates to a linear motor for lifts for driving a lift car guided in a lift shaft, having at least one stator winding row which can be fixed to the lift shaft or on the lift car and having at least one row of exciter magnets of alternating polarity which are situated opposite the stator windings at a distance and can be fixed to the lift car or on the lift shaft, respectively.
The invention relates, in addition, to a lift having a lift car which can be driven in a lift shaft.
Lifts in very high buildings should achieve high carrying capacities with as small space requirement as possible. This requirement can be fulfilled in that a multiplicity of lift cars are propelled at high velocities with low lift car weight in a lift shaft. However, a necessary condition for this is that the lift cars are driven directly without cable. Because of the considerably reduced mass during an empty journey, there is, in particular, the possibility of propelling empty lift cars at high velocity and with high acceleration and, consequently, of reducing the waiting time appreciably.
The linear motor mentioned at the outset, in particular, is suitable for the direct drive of a cable-free lift, the stator windings, which form the primary coils of the linear motor, normally being mounted on a wall of the lift shaft and the exciter magnets on the lift car. The condition imposed on the linear motor is that it has a beneficial efficiency and should load the lift car and the lift shaft wall with as little inherent mass and transverse forces as possible.
In addition, the noise developed by the linear motor is a particular problem, especially if the motor is fixed directly to the lift car. In this connection, noise and vibration are predominantly caused by grooving harmonics, by magnetostriction and by time-variable magnetic forces during the journey. Since a direct drive for lifts should have at least the same travelling characteristics and the same low noise level in the lift car as conventional high-quality cable lifts, the requirement is imposed on the linear motor drive of lifts, in particular, to generate as little vibration and noise as possible.
European Published Specification EP 0 556 595 A1 describes a passenger carrying system for very high buildings in which lift cars are used which are directly driven by means of a linear motor. The lift cars can be propelled not only in the vertical direction along the lift shaft, but additionally also in the horizontal direction by a mechanical device. Consequently, a change from one lift shaft to an adjacent lift shaft is possible, as a result of which a high carrying flow can be achieved if the change takes place very quickly. The lift car is driven with the aid of a synchronous long stator which is mounted flatly on the shaft rear wall. The corresponding exciter field is attached to the rear wall of the lift car.
A further lift driven by a liner motor is disclosed in European Patent Specification EP 0 509 647 B1. In order to achieve a high carrying capacity, said publication proposes to install in a circular manner four lift shafts and two empty shafts in total, two lift shafts being used for the upward journey and the other two for the downward journey in each case. Each shaft pair comprises in turn a local and an express track, and in a few storys, mechanical devices are provided in order to interchange the lift cars between the local and express tracks. The linear motor drive described in said European patent specification also comprises stator coils attached to the shaft rear wall and exciter magnets situated opposite the latter via an air gap and disposed on the rear wall of the lift car.
Both in the case of the passenger carrying system described in European Published Specification EP 0 556 595 A1 and in the case of the lift described in the abovementioned European patent specification, high forces of attraction act between exciter and stator and, consequently, high forces act on the lift car and on the wall of the lift shaft as a result of the design of the linear motor. This makes necessary a very robust construction of the lift car and of the attachment of the stator to the lift wall, as a result of which the mass of the lift cabin is in turn appreciably increased. In order to maintain the air gap necessary for the functioning of the linear motor between stator and exciter, at least the exciter has to be provided with spacing rollers which are mounted on the rear wall of the lift car. Because of the high contact pressure of the spacing rollers, severe vibration has to be expected. High travelling velocities are therefore only achievable to a limited extent for this reason.
A further linear-motor-driven lift system is disclosed in U.S. Pat. No. 5,183,980. A synchronous long stator and also an exciter field formed by means of permanent magnets are likewise used in the case of this lift system. On both sides, the exciter field is mounted on two metal sheets projecting from side walls of the lift car situated mutually opposite. The propulsion force is generated by four stator coils in total. The lift car is guided inside the lift shaft with the aid of the so-called zero flux method. This makes use of the effect that a displacement of the lift car in the horizonal direction perpendicularly or parallel to the laterally projecting metal sheets produces an alteration in the magnetic flux through the stator coils as a result of which the position of the lift car can in turn be corrected.
Said zero flux method has, however, the disadvantage that the guide forces necessary to guide the lift car are produced only when the lift car is travelling so that, when the lift car is stationary and when it is travelling slowly, the parts of the linear motor have to be held in a central position by heavily loaded guide rollers immediately adjacent to the linear motor and disposed on suitably robust guides. In addition, it has been found that, in the case of the linear-motor-driven lift system disclosed in U.S. Pat. No. 5,183,980, a good efficiency can be achieved only if the magnetic field strength in the air gap is high and, for this purpose, stator metal sheets for guiding the magnetic field are necessary on the side of the stator coils over the entire transportation height of the lift car. During the passage of the lift car and the exciter magnets mounted thereon, the stator metal sheets situated mutually opposite are exposed to strong dynamic forces of attraction. This results in a high loading of the entire stator construction and attachment and requires suitable measures for avoiding structure-born noise. In addition, the inherent weight of the stator metal sheets extending over the entire lift shaft length requires a very robust construction of the lift shaft.